Printer ribbon feed

ABSTRACT

A printer having a printhead which moves from left to right across the document to print a line and a ribbon located between the printing end of the printhead and the document. Ribbon supply means is provided at the right side of the document, ribbon takeup means is provided at the left side of the document and means for engaging the ribbon when the printhead moves from right to left is mounted on the printhead. During a printing operation with left-to-right movement of the printhead, the ribbon remains stationary and is traversed by the printhead. This provides a new area of the ribbon for printing each character. When the printhead returns to the left to begin a new line, printing does not occur and the engaging means connected to the printhead pulls the ribbon from the supply means. The resulting slack in the ribbon is taken up at the left side of the document by the takeup means and when the printhead reaches the left margin a new supply of ribbon has been provided for printing the next line. Since the printhead prints when moving toward the right, its velocity is slower in this direction. Preferably, the engaging means is fractionally operable to engage the ribbon at the higher speed during leftward movement but slides with respect to the ribbon at the slower velocity during rightward movement.

United States Patent 1191 'Murphy [54] PRINTER RIBBON FEED [75]Inventor: John B. Murphy, West Roxbury,

Mass.

{73] Assignee: Mohawk Data Sciences Corporation,

Herkirner, N.Y.

2'2 Filed: Mar. 3, 1971 [21 App1.No.:120,432

Primary Examiner-Robert E. Pulfrey Assistant Examiner-R. T. RaderAttorney-Francis J. Thomas, Richard H. Smith and Thomas C. Siekman 1451Apr. 10, 1973 ABSTRACT A printer having a printhead which moves fromleft to right across the document to print a line and a ribbon locatedbetween the printing end of the printhead and the document. Ribbonsupply means is provided at the right side of the document, ribbontake-up means is provided at the left side of the document and means forengaging the ribbon when the printhead moves from right to left ismounted on the printhead. During a printing operation with left-to-rightmovement of the printhead, the ribbon remains stationary and istraversed by the printhead. This provides a new area of the ribbon forprinting each character. When the printhead returns to the left to begina new line, printing does not occur and the engaging means connected tothe printhead pulls the ribbon from the supply means. The resultingslack in the ribbon is taken up at the left side of the document by thetake-up means and when the printhead reaches the left margin a newsupply of ribbon has been provided for printing the next line. Since theprinthead prints when moving toward the right, its velocity is slower inthis direction. Preferably, the engaging means is fractionally operableto engage the ribbon at the higher speed during leftward movement butslides with respect to the ribbon at the slower velocity duringrightward movement.

4 Claim, 5 Drawing Figures PATENIE APR 1 01975 SHEET 1 [IF 3 Y H P R U MB N H O J ATTORNEY PATENTEU APR 1 0 973 SHEET 3 BF 3 PRINTER RIBBON FEEDBACKGROUND OF THE INVENTION This invention relates to printers of thetype wherein an inked ribbon is moved with respect to the document sothat different areas of the ribbon may be used for printing. Moreparticularly, this invention relates to feeding an inked ribbon in sucha printer having a printhead which moves across the document to print aline.

Printers having printheads that move from the left to the right marginas they print a line, character by character, are well known. Uponcompleting a line, the printhead returns to the left margin to begin anew line while the document being printed upon is stepped to present anew blank area for printing. The necessary ink in many of these printersis provided by a ribbon located between the printhead and document. Theribbon is generally moved between locations adjacent the left and rightmargins, of the document so that fresh ink is provided for printingsuccessive lines. Such ribbon movement is often accomplished by acontinually driven take-up reel at one margin which pulls the ribbonfrom a supply reel at the other margin. In order to utilize all theribbon, it is generally moved at a slow speed so that some ribbon is notmissed during return leftward movement of the printhead. However, byfeeding it at a slow speed, some areas of the ribbon are used twice dueto the faster speed of the printhead.

Obviously, those characters printed with this already used areas of theribbon are lighter than those printed with the new ribbon. Each printedline thus contains characters of different densities.

SUMMARY OF THE INVENTION It is the primary object of this invention toprovide a printer, having a printhead which moves across the document,with a ribbon feed that allows printing of each line with characters ofuniform density.

It is a further object to provide a ribbon feed for such a printer whichis simple, reliable and inexpensive.

These objects and others are achieved by the invention according towhich a printer with a printhead that moves between two positions acrossthe document to print a line is provided with a ribbon supply means atone side of the document and ribbon take-up means at the other. Meansfor engaging the ribbon is connected to the printhead and operable onlywhen the printhead travels toward the take-up means and away from thesupply means. During this movement, the ribbon is pulled from the supplymeans and gathered at the takeup means. Generally, the printhead in sucha printer moves at a slower velocity in one direction during which itprints than in the other direction when it returns to begin a new line.Preferably, the engaging means is frictionally operable so that itengages the ribbon at the higher velocity but, at the lower velocity,the ribbon is allowed to slide with respect to it and the printhead.This allows each character of the line to be imprinted with a new supplyof ink as the printhead traverses the ribbon while printing. Uniformcharacter densities across the lines are thereby provided. As theprinthead returns to begin a new line, the ribbon is engaged and a newsupply pulled from the supply means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of aprinter incorporating a preferred embodiment of the invention.

FIG. 2 is a partial plan view of the printhead and the means connectedto the printhead for engaging the ribbon.

FIG. 3 is an elevation view of the elements shown in FIG. 2.

' FIG. 4 is a rear perspective view of the ribbon cassette (with itsrear side partially cut-away) from which the ribbon is supplied and intowhich it is taken up.

FIG. 5 is a view of the spring mechanism for returning the printhead tothe left margin.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic rear viewof a printer embodying the invention. Thus, the left margin of thedocument 1 being printed upon is designated 1a and appears at the rightside in FIG. 1. Conversely, the right margin of the document isdesignated 1b and appears at the left in FIG. 1. The printer is of thetype which prints characters, one by one, with a printhead 3 which movesacross the document 1 from its left margin In to its right margin lb.The printhead shown is of the well known matrix variety and thuscontains a plurality of styli wires which are selectively projected outof its printing end 3a in patterns which form the characters on thedocument 1 as it moves from the left to the right margin (toward theleft in FIG. 1). When printing, the styli wires force an inked ribbon 7against the document 1 and a platen 5 located in back of the document toform their impressions. After printing each line, the printhead isreturned to the left margin 1a to initiate a new line. During thiscarriage return movement, the document 1 is stepped (by means not shown)a one line increment so that a new blank area is provided for printing.

A motor 9 is provided for moving the printhead toward the right marginlb when printing. This drive motor could also be utilized by appropriatemeans to step the document 1 after each line is printed. However, thedocument stepping means is not shown in FIG. 1 since any conventionalapparatus could be utilized. The output shaft 11 of drive motor 9 havingflywheel l3 thereon drives a pulley 14 via another pulley 12 and a belt15. Pulley 14 via shaft 16 and worm l7 drives gear 18 which is connectedto a driving gear 21 via shaft 20, clutch l9, and shaft 22. The motor 9continually drives gear 18 and the clutch 19 is selectively operable toeffect rotation of the driving gear 21. A toothed belt 23 is drivinglyconnected around the peripheries of the driving gear 21 and a furthergear 26 to drivingly connect the two. The printhead 3 is connected tobelt 23 by member 24 on which the printhead is mounted and which isrigidly attached to belt 23. Gears 21 and 26 are spaced apart atopposite ends of the document and, with the printhead attached to belt23, rotation of these gears causes the printhead to move back and forthacross the document 1 being printed upon. A pair of guide bars, 24a and24b are slidably located through the mounting member M to guide movementadjacent to gear 26.

A spring mechanism 25 is mounted adjacent to gear 26. FIG. 5 shows thespring mechanism from the rear of the printer similar to the view ofFIG. 1. Referring to both these FIGS., the mechanism 25 comprises ahousing 25b within which a helical spring 25a is located. A shaft 27extends through the spring mechanism 25 and is connected to gear 26 torotate therewith. Within the housing 25b, the shaft 27 has a keyway 27a(FIG. 5) within which one end of the spring 25a is secured. The otherend of the spring 25a is connected to the housing 25b which, in turn, isheld fixed by a mount 32 on a base 34. With the shaft 27 connected togear 26, counter-clockwise rotation of the gear winds up the spring 25a.

During operation of the printer, the drive motor 9 continually operatesto drive gear 18 and, when clutch 19 is engaged, gear 21 is rotatedcounter-clockwise (in FIG. 1) to move belt 23 around gears 21 and 26. Asthe gears rotate counter-clockwise, the printhead moves from the left lato the right lb margin of the document 1. During this movement of theprinthead, a line of characters is printed on the document and spring25a is wound due to the rotation of shaft 27 from gear 26. After theline has been printed and the printhead has reached the right margin 1bof the document, light from the light source 2a normally received by aphotocell 4a is interrupted by a shutter 6 mounted to the printheadmounting 24. The resulting change in the photocells output is utilizedby appropriate circuitry to disengage clutch 19. When disengaged, theclutch 19 allows gear 21 to freely rotate and due to the force of spring25a gears 26 and 21 are caused to rotate clockwise and the printhead 3is carried to the left margin 1a of the document. Just after reachingthis left margin, the shutter 6 interrupts light between a secondphotocell 4b and light source 2b. The resulting change in the output ofphotocell 4b appropriate circuitry to now engage the clutch 19. Thisobviously causes gear 21 to begin to rotate counter-clockwise andinitiate printhead movement toward the left in FIG. 1 during whichprinting occurs.

The circuitry for controlling the clutch 19 in response to thephotocells 2a and 2b is not shown or described since any suitableconventional circuit may be utilized and such a circuit forms no part ofthe invention. Similarly, the printhead itself and the circuits forcontrolling it are not illustrated since any suitable well knownelements could be utilized and these do not form a part of theinvention.

Referring again to FIG. 1, the printer contains a ribbon cassette 31 forproviding the ribbon 7, which is endless, from its supply end 31alocated adjacent the right margin lb of the document. A. shown, theribbon is guided in a path from the supply end 31a, to around theprinthead 3 and, thereafter, to the opposite end 31b of the cassette. Atthe printhead, the ribbon is engaged such that during movement by theprinthead to the right margin lb the printhead slides with respect tothe ribbon. However, during movement of the printhead towards the leftmargin la, the ribbon is engaged at the head and pulled from the supplyend 31a of the cassette. This obviously causes slack in the ribbon atthe cassettes take-up end 31b which is taken care of by a ribbon drivegear 29 mounted on the shaft 27. As previously disclosed, shaft 27revolves with printhead movement to the left margin during carriagereturn. Ribbon drive gear 29 thus rotates during this time and engages agear 43 shown in FIG. 4 to cause the slack ribbon to be taken-up intothe cassette 31.

A mechanical one-way clutch 29a is provided between gear 29 and theshaft 27 so that the ribbon drive gear 29 is not rotated duringprinthead movement to the right margin. The clutch 29a allows the gearto become drivingly engaged with shaft 27 only when the shaft is beingrotated (clockwise in FIG. 1) by the spring mechanism 25 during carriagereturn when ribbon slack occurs at the left margin and rotation of gear29 is desired. Any appropriate one-way clutch may be used.

Referring to FIG. 4 which illustrates the cassette with its back side 73partly cut-away, gear 43 is mounted at the end of a first pinch roller47 which cooperates with a second pinch roller 42 to engage the ribbonbetween them and pull it into the cassette during carriage return.However, during printhead movement to the left margin, the two rollersoperate to hold the ribbon stationary as it is traversed by theprinthead. Between its supply end 31a and take-up end 31b the ribbon isstored in a series of vertical loops. At the supply end, the ribbontravels through an outlet passageway (not 'shown) from which it ispulled by the printhead. This outlet passageway and the inlet passageway(also not shown) at end 31b of the cassette are merely holes in the rearside 44 of the cassette. At the input end 31b, the ribbon 7 enters theinput passageway, turns 90, and then travels downwardly to becomeengaged between rollers 42 and 47. At the output end 31a, the ribbon 7passes between a spring 46 and a guide 48, turns 90, and thereafterpasses out of the outlet passageway of the cassette. A spring 46 andguide 48 pinch the ribbon between them so that the ribbon may be pulledfrom the cassette with a constant tension.

As shown in FIG. 1, the ribbon at the printhead takes a substantiallyU-shaped form since it travels around the printing end 3a of theprinthead and passes around a pair of pins 35 located on opposite sidesof the printhead 3 but disposed away from the printing end 3a. FIGS. 2and 3 show the ribbon engaging means located at the printhead whichcauses the ribbon to take this path. The engaging means frictionallyengages the ribbon during carriage return but allows the ribbon to slipwith respect to it and the printhead during the printing operation. Thisaction is achieved by and dependent upon the speed with which theprinthead is moved across the document. When printing, the printheadnecessarily moves at a slower velocity than during carriage return. Atthis slower speed, slippage occurs while the higher speed of theprinthead during carriage return causes the ribbon to be frictionallyengagedv With the preferred embodiment disclosed, it has been found thatwhen the printhead is moved to print across the document from leftmargin 1a to right margin 1b at a relatively constant speed of 10 inchesper second and, thereafter, returned to the left margin constantlyaccelerating from a zero velocity at the right margin lb to a maximumvelocity of approximately inches per second at the left margin, theengaging means illustrated frictionally engages the ribbon duringcarriage return yet slips with respect to the ribbon during the printingoperation. During carriage return, the

ribbon becomes engaged and pulled when the printhead reaches thevelocity of inches per second.

These results were obtained with a conventional nylon ink ribbon andpins 35 and printhead 3 made of steel.

As noted above, during carriage return when the ribbon is engaged at theprinthead, it is pulled from the output end 31a of the cassette and anew length of ribbon is provided for the next line. Since the ribbon isnot instantaneously engaged at the start of the carriage return and theprinthead must first achieve sufficient velocity (i.e., l5 ips), theribbon pulled from the supply end of the cassette 31a is not exactly thelength required to print a succeeding line. Thus, as indicated above,the output of photocell 4b is changed just after the printhead reachesthe right margin la on carriage return. This allows a small additionallength of ribbon pin. The printing end 3a of the printhead is aboutfiveeighth inch wide and the pins are located about 1 %inches from theprinting end 3a.

The ribbons path between the pins 35 and loops 43a and 45a is on anangle of about 15 with respect to the centerline of the printhead.Further, the points on the loops (43a and 45a) contacted by the ribbonare approximately two-sixteenth inch from the printing end of theprinter. Also, the width of the ribbon is one-half inch and about halfof it is in contact with the printing end 30 of the printhead (as shownin FIG. 3).

It will be appreciated that various changes in the form and details ofthe above-described preferred emto be pulled from the cassette making upthe slippage which occurred when the carriage return was firstinitiated. Changing of the photocells 4b output at this time mayobviously be achieved by placing it and its cooperating light 2b a smalldistance to the right (as shown in FIG. 1) of the left margin 1a.

FIGS. 2 and 3 show in detail the means at the located on opposite sidesof the printhead 3 and the pins 35 project upwardly therefrom. As shownin FIG.

3, each pin 35 has a head 37 at its top and a flange 39 at its bottomwhere it is connected to ear 33. These heads 37 and flanges 39 help toguide the ribbon should it slip vertically at the pins 35.

FIGS. 2 and 3 also show a guide attached at the printing end of theprinthead. This guide comprises a bottom 41, and two sides, 43 and 45,projecting from the bottom 41. As most clearly shown in FIG. 2, theprinthead projects over bottom 41 and between sides 43 and 45. Sides 43and 45 and bottom 41 are shaped to correspond to the printheads shape atits printing end. As shown from FIGS. 2 and 3, sides 43 and 45 terminatea distance away from the printing end 3a of the. printer in loops 43aand 45a respectively. Loops 43a and 45a provide smooth surfaces for theribbon to traverse from pins to around the printhead 30. As also shownin FIGS. 2 and 3, the sides 43 and each have a pair of top and bottomflanges. Side 45 has top flange 45b and bottom flange 450 while,similarly, side 43 has top flange 43b and bottom flange 43c. Theseflanges serve as safety guides so that if the ribbon 7 is displacedvertically from the printhead it is caught and thereafter guided by thetop or bottom pair of flanges. Thus, the guide at the end of theprinthead shown in FIGS. 2 and 3 together with the pins 35 at the sidesof the printhead which project from ears 33 serve to guide the ribboninto a U-shaped form around the printing end 3a of the printhead and tofrictionally engage the ribbon at the printheads higher speed whileallowing the ribbon to slip around its U-shaped form at the printheadsslower speed.

Although the ribbon engaging means shown in FIGS. 2 and 3 is preferred,there obviously are many possible arrangements which could serve tofrictionally engage the ribbon at the higher velocity of the printheadwhile allowing slippage at the lower velocity. In the embodiment shown,the pins each have a diameter of about three-sixteenth inch, are locatedabout 1.4 inches apart and the ribbon makes about a wrap around eachbodiment may be effected by persons of ordinary skill without departingfrom the true spirit and scope of the invention.

Iclaim:

1. In a printer having a reciprocating carriage for generating linearrelative movement between a print medium and a print mechanism andfurther including print control means for causing the print mechanism toprint a line of characters on the print medium during movement of saidcarriage in a first direction, ink ribbon handling means comprising, incombination:

a case containing a loosely folded supply of ink ribbon with a length ofsaid ribbon extending outside of said case through a first slot providedin a side thereof;

drag means acting against said ribbon in an area adjacent said slot;

ribbon guide means supporting said outside-extending length of ribbonalong a path lying between said print medium and said print mechanism, aportion of said guide means being mounted on said print mechanism andincluding at least one relatively sharp edge projecting into the ribbonpath; take-up means for holding said ribbon stationary during movementof said carriage in said first direction;

means for moving said carriage in said first direction at a firstvelocity and for accelerating said carriage in the return directionafter completion of said line of printing, whereby the frictional forceexerted on said ribbon by said guide means during carriage returnexceeding the friction force exerted by said drag means thereby causingsaid guide means to pull an additional length of ribbon out of said caseduring said return movement; and

said takeup means taking up the slack in said ribbon caused by thepulling of said ribbon during said return movement.

2. The printer set forth in claim 1 wherein said print mechanism isfixed to and moves with said carriage and said print medium and saidcase remain stationary during the printing operation.

3. The printer set forth in "claim 1 wherein said takeup meanscomprises:

a pair of pinch rolls acting on the ribbon; and

means driven by said carriage moving means for rotating said pinch rollsduring the return movement of said carriage.

4. The printer set forth in claim 1 wherein:

said ribbon is in the form of an endless band; and

said takeup means operates to feed the ribbon back into said casethrough a second slot provided on a side of said case opposite saidfirst slot.

1. In a printer having a reciprocating carriage for generating linearrelative movement between a print medium and a print mechanism andfurther including print control mEans for causing the print mechanism toprint a line of characters on the print medium during movement of saidcarriage in a first direction, ink ribbon handling means comprising, incombination: a case containing a loosely folded supply of ink ribbonwith a length of said ribbon extending outside of said case through afirst slot provided in a side thereof; drag means acting against saidribbon in an area adjacent said slot; ribbon guide means supporting saidoutside-extending length of ribbon along a path lying between said printmedium and said print mechanism, a portion of said guide means beingmounted on said print mechanism and including at least one relativelysharp edge projecting into the ribbon path; take-up means for holdingsaid ribbon stationary during movement of said carriage in said firstdirection; means for moving said carriage in said first direction at afirst velocity and for accelerating said carriage in the returndirection after completion of said line of printing, whereby thefrictional force exerted on said ribbon by said guide means duringcarriage return exceeding the friction force exerted by said drag meansthereby causing said guide means to pull an additional length of ribbonout of said case during said return movement; and said takeup meanstaking up the slack in said ribbon caused by the pulling of said ribbonduring said return movement.
 2. The printer set forth in claim 1 whereinsaid print mechanism is fixed to and moves with said carriage and saidprint medium and said case remain stationary during the printingoperation.
 3. The printer set forth in claim 1 wherein said takeup meanscomprises: a pair of pinch rolls acting on the ribbon; and means drivenby said carriage moving means for rotating said pinch rolls during thereturn movement of said carriage.
 4. The printer set forth in claim 1wherein: said ribbon is in the form of an endless band; and said takeupmeans operates to feed the ribbon back into said case through a secondslot provided on a side of said case opposite said first slot.